Wheelchair system with motion sensors and neural stimulation

ABSTRACT

A system and method for improving stability of a wheelchair user includes a wheelchair having sensors measuring motion parameters to sense collisions and sharp turns which may unseat the user. Neuromuscular stimulating electrodes attached to extensor and flexor muscles of the user&#39;s trunk and under the command of a controller in communication with the sensors activate the muscles during turns and collisions to counteract the forces induced. A system and method for increasing manual propulsion efficiency includes sensors for sensing motion parameters indicating completion of a manual push of the wheelchair wheels and recovery from the push. Neuromuscular stimulating electrodes attached to extensor and flexor muscles of the user&#39;s trunk and under the command of a controller in communication with the sensors activate the muscles at the appropriate time in the cycle of push and recovery.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims priority to U.S. ProvisionalApplication No. 62/541,879, filed Aug. 7, 2017 and hereby incorporatedby reference.

FIELD OF THE INVENTION

This invention relates to wheelchairs having inertial sensors forproviding information used to control neural stimulation of thewheelchair user.

BACKGROUND

For people with spinal cord injuries who have lost the ability tocontrol their trunk muscles, minor disturbances, such as a sharp turn ora collision with a curb, can destabilize the user and cause a loss oferect sitting posture, potentially leading to injurious falls. Falls arein fact the leading cause of injury for wheelchair users, and accountfor over 66,000 wheelchair related injuries per year. The injuries canbe serious and include lacerations, contusions, abrasions, fractures andcan result in death. According to at least one survey of people havingspinal cord injuries, trunk stability is among the top functions theywould like to see restored. There is clearly an opportunity to improvethe safety of wheelchair users by increasing trunk stability.

Loss of control of trunk muscles also reduces the efficiency of manualpropulsion of wheelchairs. Wheelchair users with poor trunk control dueto paralysis of core thigh, hip and trunk muscles have limited trunkstability and may be unable to fully or safely lean backward andforward, resulting in inefficient pushing of the wheelchair. Theinability to efficiently propel the wheelchair can make traversingchallenging terrain, such as inclined ramps, difficult and can also leadto shoulder injuries. There is clearly an opportunity to improve theefficiency of wheelchair propulsion by increasing or restoring a degreeof trunk control.

SUMMARY

The invention concerns a wheelchair system providing neural stimulationto a user. In one example embodiment the system comprises a wheelchair.A sensor is positioned on the wheelchair for measuring a motionparameter thereof and generating one or more signals indicative of themotion parameter. A plurality of neural stimulating electrodes areattached to the user, each electrode attached to a respective muscle ofthe user for activating the respective muscle. A controller is incommunication with the sensor and is adapted to receive the signals. Thecontroller is also in communication with the plurality of electrodes foractivating selected ones of the respective muscles in response to thesignals.

The controller may be mounted on the wheelchair or the user. The motionparameter may comprise a linear motion parameter. The linear motionparameter is oriented in a direction of motion of the wheelchair and maybe selected from the group consisting of linear velocity, linearacceleration and combinations thereof. The electrodes are attached tomuscles selected from the group consisting of erector spinae, quadratuslumborum, gluteus maximus, posterior adductor and combinations thereof.The electrodes may be implanted beneath the user's skin or on a surfaceof the user's skin. The motion parameter may also comprise an angularmotion parameter. The angular motion parameter is oriented about aturning axis of the wheelchair and may be selected from the groupconsisting of angular acceleration, angular velocity, and combinationsthereof. The electrodes are attached to muscles selected from the groupconsisting of right erector spinae, right quadratus lumborum, rightgluteus maximus, right posterior adductor, left erector spinae, leftquadratus lumborum, left gluteus maximus, left posterior adductor andcombinations thereof. The electrodes may be implanted beneath the user'sskin or mounted on a surface of the user's skin.

In an example embodiment the sensor comprises an inertial measurementunit. Further by way of example, the sensor comprises at least onegyroscope and at least one accelerometer. In another example, the sensorcomprises a radio frequency transmitter for wirelessly transmitting thesignals to the controller. In an example embodiment the controllercomprises a radio frequency receiver for receiving the signals and amicroprocessor in communication with the receiver. In another example aseat belt controlled by a motor is mounted on the wheelchair. Thecontroller controls the motor for tightening the belt. Further by way ofexample, a brake, controlled by an actuator, is mounted on thewheelchair, the controller controlling the actuator for applying thebrake. In another example a distress indicator controlled by thecontroller for broadcasting a distress call.

The invention also encompasses a method of providing neural stimulationto a user of a wheelchair based upon motion of the wheelchair. In oneexample embodiment the method comprises:

-   -   measuring a motion parameter of the wheelchair;    -   generating a signal indicative of the motion parameter;    -   evaluating the signal;    -   activating at least one muscle of the user in response to the        signal.

In one example, measuring the motion parameter comprises measuring alinear velocity of the wheelchair. By way of example, measuring themotion parameter comprises measuring a linear acceleration of thewheelchair or measuring an angular acceleration of the wheelchair ormeasuring an angular velocity of the wheelchair. By way of example,generating a signal comprises generating a signal indicative of at leastone motion parameter selected from the group consisting of a linearvelocity, a linear acceleration, an angular velocity, an angularacceleration, and combinations thereof. By way of example, evaluatingthe signal comprises converting the signal to a value indicative of amagnitude of the motion parameter and comparing the magnitude to athreshold magnitude of the motion parameter. In another example,evaluating the signal comprises converting the signal to a valueindicative of a direction of the motion parameter and comparing thedirection to a reference direction.

In an example embodiment, activating at least one muscle of the user inresponse to the signal comprises selecting one or more muscles of theuser and applying a neural stimulus to activate the one or more muscles.By way of example, selecting one or more muscles of the user comprisesselecting the erector spinae, quadratus lumborum, gluteus maximus, andposterior adductor muscles when the motion parameter is a linearacceleration which exceeds a threshold value. Further by way of example,selecting one or more muscles of the user comprises selecting righterector spinae, right quadratus lumborum, right gluteus maximus, andright posterior adductor muscles when the motion parameter is an angularacceleration or an angular velocity in a counterclockwise directionabout a turning axis. Also by way of example, selecting one or moremuscles of the user comprises selecting left erector spinae, leftquadratus lumborum, left gluteus maximus, and left posterior adductormuscles when the motion parameter is an angular acceleration or anangular velocity in a clockwise direction about a turning axis.

The invention also encompasses method of providing neural stimulation toa user of a wheelchair based upon motion of the wheelchair during acollision. In an example embodiment the method comprises:

-   -   monitoring linear acceleration in a direction of motion of the        wheelchair;    -   calculating a moving root mean square of the linear acceleration        and comparing it against a first predetermined threshold value;    -   comparing a derivative of the root mean square linear        acceleration against a second predetermined threshold value;    -   calculating a change in velocity using the linear acceleration        and comparing the change in velocity to a third predetermined        threshold value;    -   applying neuromuscular stimulation if the first, second and        third predetermined threshold values are exceeded within a        predetermined time period.

An example method of applying a restraint to a user of a wheelchairbased upon motion of the wheelchair is also contemplated and comprises:

-   -   measuring a motion parameter of the wheelchair;    -   generating a signal indicative of the motion parameter;    -   evaluating the signal;    -   activating at least one the restraint in response to the signal.

By way of example, measuring the motion parameter comprises measuring alinear velocity of the wheelchair, measuring a linear acceleration ofthe wheelchair measuring an angular acceleration of the wheelchair ormeasuring an angular velocity of the wheelchair. In an exampleembodiment, generating a signal comprises generating a signal indicativeof at least one the motion parameter selected from the group consistingof a linear velocity, a linear acceleration, an angular velocity, anangular acceleration, and combinations thereof.

In an example method, evaluating the signal comprises converting thesignal to a value indicative of a magnitude of the motion parameter andcomparing the magnitude to a threshold magnitude of the motionparameter. Also by way of example, evaluating the signal comprisesconverting the signal to a value indicative of a direction of the motionparameter and comparing the direction to a reference direction. Furtherby way of example, activating at least one restraint in response to thesignal is selected from the group consisting of tightening a beltsecuring the user to the wheelchair, applying a brake to slow thewheelchair, broadcasting a distress signal and combinations thereof.

The invention further encompasses a system for providing assistance to auser for manual propulsion of a wheelchair. In one example embodimentthe system comprises at least one sensor positioned on the user formeasuring a motion parameter of the user while propelling thewheelchair. The at least one sensor generate one or more signalsindicative of the motion parameter. A plurality of neural stimulatingelectrodes are positioned on the user, each electrode is attached to arespective muscle of the user for activating the respective muscle. Acontroller is in communication with the at least one sensor and adaptedto receive the signals. The controller is also in communication with theplurality of electrodes for activating selected ones of the respectivemuscles in response to the signals. In one example embodiment thecontroller is mounted on either the wheelchair or the user. By way ofexamome, at least one sensor is mounted on the user in a positionselected from the group consisting of an upper trunk of the user, ashoulder of the user, an arm of the user, a wrist of the user, a head ofthe user and combinations thereof. Further by way of example, the motionparameter is selected from the group consisting of a position of a partof the user, an acceleration of a part of the user, a rate of change ofacceleration of a part of the user, an electrical potential of a muscleof the user, and combinations thereof. By way of example, the part ofthe user is selected from the group consisting of an upper trunk of theuser, a shoulder of the user, an arm of the user, a wrist of the user, ahead of the user and combinations thereof. In an example embodiment, theelectrodes are attached to muscles selected from the group consisting ofhip flexor muscles, hip extensor muscles, trunk flexor muscles, trunkextensor muscles, abdominal muscles and combinations thereof. By way ofexample, the electrodes are implanted beneath the user's skin or aremounted on a surface of the user's skin.

In an example embodiment, the at least one sensor comprises an inertialmeasurement unit. Further by way of example, the at least one sensorcomprises at least one accelerometer. In another example, the at leastone sensor comprises at least one electromyographic sensor. Also by wayof example, the at least one sensor comprises a radio frequencytransmitter for wirelessly transmitting the signals to the controller.

The invention also encompasses a method of providing assistance to auser for manually propelling a wheelchair. In one example embodiment,the method comprises:

-   -   detecting when the user has recovered from a previous push of        the wheels of the wheelchair;    -   the user executing a next push of the wheels;    -   applying neural stimulation to trunk and hip flexor muscles of        the user while the user executes the next push of the wheels;    -   detecting when the user has completed the next push of the        wheels;    -   removing neural stimulation to the trunk and the hip flexor        muscles of the user when the user has completed the next push of        the wheels;    -   the user recovering from the next push of the wheels;    -   applying neural stimulation to trunk and hip extensor muscles of        the user while the user is recovering from the next push of the        wheels;    -   detecting when the user has recovered from the next push of the        wheels;    -   removing neural stimulation from the trunk and the hip extensor        muscles of the user when the user has recovered from the next        push of the wheels.

In an example embodiment, detecting when the user has recoveredcomprises measuring a motion parameter of a part of the user while theuser is recovering. In an example embodiment, the motion parameter isselected from the group consisting of a position of a part of the user,an acceleration of a part of the user, a rate of change of accelerationof a part of the user, an electrical potential of a muscle of the userand combinations thereof. In an example embodiment, the part of the useris selected from the group consisting of an upper trunk of the user, ashoulder of the user, an arm of the user, a wrist of the user, a head ofthe user, and combinations thereof.

By way of example, detecting when the user has completed the push of thewheels comprises measuring a motion parameter of the user while the useris pushing the wheels. In an example embodiment, the motion parameter isselected from the group consisting of a position of a part of the user,an acceleration of a part of the user, a rate of change of accelerationof a part of the user, an electrical potential of a muscle of the userand combinations thereof. Further by way of example, the part of theuser is selected from the group consisting of an upper trunk of theuser, a shoulder of the user, an arm of the user, a wrist of the user, ahead of the user, and combinations thereof. In an example embodiment,detecting when the user has recovered comprises measuringanterior-posterior acceleration of a wrist of the user. Further by wayof example, the method comprises measuring a rate of change of theanterior-posterior acceleration. Also by way of example, the methodcomprises measuring a rate of change of a medial-lateral acceleration ofthe wrist. In an example embodiment, detecting when the user hascompleted the push comprises measuring anterior-posterior accelerationof a wrist of the user. By way of example, the method may also comprisemeasuring a rate of change of the anterior-posterior acceleration. Anexample embodiment further comprises measuring a medial-lateralacceleration of the wrist.

In an example embodiment, detecting when a user has completed a push ofthe wheels comprises:

-   -   detecting an acceleration signal indicative of        anterior-posterior acceleration of a part of the user greater        than a predetermined threshold value;    -   detecting an increasing rate of change of the acceleration        signal;    -   detecting a medial-lateral acceleration of the part of the user        within a predetermined range of values.

By way of example, detecting when a user has recovered from a push ofthe wheels comprises:

-   -   detecting an acceleration signal indicative of        anterior-posterior acceleration of a part of the user less than        a predetermined threshold value;    -   detecting a decreasing rate of change of the acceleration        signal;    -   detecting a medial-lateral acceleration of the part of the user        having an increasing rate of change.

In an example embodiment, the part of the user comprises a wrist.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric rear view of an example wheelchair system forstabilizing a user according to the invention;

FIG. 2 is an isometric side view of the wheelchair system shown in FIG.1;

FIG. 3 is a flow chart illustrating an example method of stabilizing auser according to the invention;

FIG. 4 is a flow chart illustrating an example method of stabilizing auser according to the invention;

FIG. 5 is a flow chart illustrating an example method of stabilizing auser according to the invention;

FIG. 6 is an isometric side view of another example embodiment of awheelchair system for stabilizing a user according to the invention;

FIG. 7 is an isometric front view of an example embodiment of awheelchair system for increasing propulsion efficiency of a useraccording to the invention;

FIGS. 8-14 are schematic representations showing stages in the cycle ofa user propelling the wheelchair system shown in FIG. 7;

FIG. 15 is a flow chart illustrating an example method of increasing thepropulsion efficiency of a wheelchair according to the invention; and

FIG. 16 is a flow chart illustrating an example method of increasing thepropulsion efficiency of a wheelchair according to the invention.

DETAILED DESCRIPTION

FIGS. 1 and 2 show an example embodiment of a wheelchair system 10according to the invention. System 10 comprises a wheelchair 12. Amotion sensor 14 is positioned on the wheelchair 12. Motion sensor 14measures one or more motion parameters of wheelchair 12 and generatessignals indicative of the motion parameters. In an example embodimentthe sensor 14 may be an inertial measurement unit (IMU) includingaccelerometers for measuring motion parameters such as acceleration ofthe wheelchair 12 in three mutually perpendicular axes (X, Y and Z asdefined in FIG. 1) as well as one or more gyroscopes for measuringmotion parameters such as angular velocity and angular acceleration ofthe wheelchair about the axes X, Y and Z. The sensor 14 also includes aradio frequency transmitter 16 used to transmit the signals wirelessly.A controller 18 is also part of system 10. In this example thecontroller 18 is also mounted on the wheelchair 12 but in anotherembodiment may be worn by (mounted on) the user 20. In the exampleembodiment shown controller 18 comprises a radio frequency receiver 22for receiving signals from the sensor 14, and a microprocessor 24 incommunication with receiver 22. The microprocessor may be, for example,a programmable logic controller. Software resident in the microprocessor24 evaluates the signals from the sensor 14 and directs themicroprocessor to issue commands to one or more of a plurality of neuralstimulating electrodes 26, also part of system 10. Communication betweencontroller 18 and electrodes 26 may be via wires or wirelessly.

Electrodes 26 are attached to respective muscles (detailed below) of theuser 20 and selected ones are activated in response to the signalsaccording to algorithms encoded in the software in the microprocessor24. Electrodes 26 can be mounted on the surface skin of the user 20using transcutaneous electrical nerve stimulation equipment (TENS) orimplanted beneath the skin, using intramuscular implants or nerve cuffelectrodes. In an experimental setting, an example system 10 used 8, 12or 16 channel IPGs to deliver asymmetrical charged-balanced currentcontrolled stimulus waveforms with pulse amplitudes (0-20 mA) selectablefor each channel and variable pulse durations (0-250 μsec) andfrequencies (0-20 Hz) set on a pulse by pulse basis.

The wheelchair system 10 according to the invention helps prevent user20 from falling out of wheelchair 12 when unexpected destabilizingevents, such as collisions or sharp turns, are encountered duringeveryday activities. This goal is accomplished by using the controller18 to stimulate and thereby activate selected muscles and muscle groups(over which user 20 has lost control due to a spinal cord injury) inresponse to the motion parameters measured by sensor 14 and evaluated byalgorithms in the software of the controller 18. When activated, theselected muscles restore trunk stability appropriately in response tothe particular destabilizing event.

For collisions, such as when the wheelchair 12 encounters a curb, alinear motion parameter in the direction of wheelchair motion is used todetermine muscle activation. Example linear motion parameters used bythe controller 18 and measured by sensor 14 may be linear velocity,linear acceleration, or a combination of the two. The selected musclesto be activated by electrodes 26 in response to a collision are selectedfrom knee, hip and trunk extensor muscles and include the erectorspinae, the quadratus lumborum, the gluteus maximus, the posterioradductor and combinations thereof.

For sharp turns, an angular motion parameter oriented about a turningaxis (axis Z in FIG. 1) of wheelchair 12 is used to determine muscleactivation. Example angular motion parameters used by the controller andmeasured by sensor 14 include angular acceleration, angular velocity,and combinations of the two. The selected muscles to be activated byelectrodes 26 in response to a sharp turn are again selected from knee,hip and trunk extensor muscles, but are separated laterally, with theright erector spinae, right quadratus lumborum, right gluteus maximus,and right posterior adductor muscles being selected when the motionparameter is an angular acceleration or an angular velocity in acounterclockwise direction about the Z axis, and the left erectorspinae, left quadratus lumborum, left gluteus maximus, and leftposterior adductor muscles being selected when the motion parameter isan angular acceleration or an angular velocity in a clockwise directionabout the Z axis.

The invention also encompasses a method of providing neural stimulationto the user 20 of wheelchair 12. FIG. 3 shows a flowchart illustratingan example method, which comprises:

-   -   measuring a motion parameter of the wheelchair (28);    -   generating a signal indicative of the motion parameter (30);    -   evaluating the signal (32); and    -   activating at least one muscle of the user in response to the        signal (34).

As noted above, measuring the motion parameter of the wheelchair 12includes measuring a linear acceleration and/or linear velocity (for acollision for example) and measuring the angular velocity and/or angularacceleration of the wheelchair about a turning axis (for sharp turns forexample). Generating a signal includes generating a signal, for example,a voltage signal, indicative of any of the motion parameters including alinear velocity, a linear acceleration, an angular velocity, an angularacceleration, and combinations thereof.

Evaluating the signal for a collision event comprises converting thesignal to a value indicative of the magnitude of the motion parameterand then comparing that magnitude to a known threshold value at whichmuscle stimulus should be applied. Effective threshold values are knownfrom experiment to vary with each wheelchair user, and in experimentalapplications of the method, collision acceleration thresholds rangingfrom 3.05 g to about 3.76 g were identified for determining when musclestimulus should be applied to the extensor muscles to resist forwardflexion to stabilize the user and assist return to upright sittingduring the collision.

For a turning event, evaluating the signal required determining thedirection of the turn as well as its magnitude. Determining the turndirection comprises comparing the measured direction to a referencedirection to determine whether to activate the left or right musclegroups. Experimental angular motion parameter magnitude thresholds fordetermining when to apply the muscle stimulus ranged from about 97degrees/sec to about 100 degrees/sec for applying muscle stimulationduring turns.

The step of activating at least one muscle, the muscle or muscle groupis selected based upon the measured motion parameters and the neuralstimulus is applied to the selected muscles appropriate for the event(collision or turn). As noted above for an example embodiment, theerector spinae, quadratus lumborum, gluteus maximus, and posterioradductor muscles are selected when the measured motion parameter is alinear acceleration (indicating a collision) which exceeds a thresholdvalue. For a measured angular motion parameter indicating a left turnand which exceeds a threshold value, one or more muscles comprises theright erector spinae, the right quadratus lumborum, the right gluteusmaximus, and the right posterior adductor muscles are selected. For ameasured angular motion parameter indicating a right turn and whichexceeds a threshold value, one or more muscles comprising the lefterector spinae, the left quadratus lumborum, the left gluteus maximus,and the left posterior adductor muscles are selected.

FIG. 4 illustrates a detailed example method according to the inventionused during a collision. In this example, the linear acceleration in thedirection of motion of the wheelchair (axis X, anterior/posterioracceleration) is monitored (36) using the sensor 14 and controller 18.Once motion is detected, algorithms 38, 40 and 42 within the controller18 begin monitoring the signals from the sensor 14 to detect acollision. Algorithm 38 calculates the moving root mean square of theanterior/posterior acceleration continually and compares it against athreshold. Algorithm 40 compares the derivative of the RMSanterior/posterior acceleration against a threshold. Algorithm 42calculates the change in velocity (integral of acceleration) andcompares that to a threshold. If the thresholds are exceeded within apredetermined time period, T1, then a crash has occurred and theappropriate neuromuscular stimulation is applied by the controller 18via electrodes 26.

FIG. 5 illustrates another example embodiment of the method according tothe invention which comprises the steps of:

-   -   measuring a motion parameter of the wheelchair (44);    -   generating a signal indicative of the motion parameter (46);    -   evaluating the signal (48); and    -   activating at least one user restraint in response to the signal        (50).

The method steps are similar to those for applying neuromuscularstimulation as described above, the difference being that a mechanicalrestraint is applied instead of muscular stimulation. As shown in FIG. 6the restraints may include applying a brake 52, tightening a seat belt54 to restrain user 20, and/or broadcasting a distress signal from aspeaker 56 or over a radio frequency transmitter 58. Activation of thevarious restraints is effected by the controller 18 via appropriateinterfaces, such as a servomotor 60 to tighten the seat belt, or anactuator 62, such as a solenoid, to apply the brake. The variousmechanical devices used with the system 10 are advantageouslyelectrical, to permit the system to be operated by a battery 64.

FIG. 7 shows another system 66 which improves the efficiency of manuallypropelled wheelchairs 68. System 66 is advantageous for users 70 withpoor trunk control due to paralysis of core, thigh, hip and trunkmuscles. Such users have limited trunk stability and are either unableto fully lean backward and forward when pushing the wheels 72 or areunsafe when doing so. This condition leads to inefficient pushing andthus difficulty in traversing challenging terrain such as inclinedramps.

System 66 comprises at least one sensor 74 positioned on user 70 formeasuring a motion parameter of the user while the user is propellingthe wheelchair 68. Motion parameters which are useful in system 66include a position of a part of the user, an acceleration of a part ofthe user, a rate of change of acceleration of a part of the user as wellas an electrical potential of a muscle of the user. One or more sensors74 may be advantageously positioned on the user's upper trunk 76,shoulder 78, arm 80, in particular wrist 82, and head 84 for measuringthe motion parameters of one or more of these parts of user 70. When itis desired to use electrical potential of a muscle as a motion parameterit is advantageous to use an electromyographic sensor mounted on theshoulder 78. Sensor 74 generates one or more signals indicative of themotion parameter while the user is propelling wheelchair 68.

In this example embodiment, one motion sensor 74 is used. Sensor 74comprises a tri-axial accelerometer, such as a commercially availableactivity tracker, and is worn on the wrist 82. The wrist accelerometer74 has a radiofrequency transmitter which transmit the signalsindicative of the selected motion parameters wirelessly to a controller86. Controller 86 may be worn by (mounted on) the user 70 or mounted onthe wheelchair 68 (shown). In the example embodiment shown, controller86 comprises a radiofrequency receiver 88 for receiving signals from thesensors 74, and a microprocessor 90 in communication with receiver 88.The microprocessor may be, for example, a programmable logic controller.Software resident in the microprocessor 90 evaluates the signals fromthe sensors 74 and directs the microprocessor to issue commands to oneor more of a plurality of neural stimulating electrodes 92, also part ofsystem 66.

Electrodes 92 are attached to respective muscles (detailed below) of theuser 70 and selected ones are activated in response to the signalsaccording to algorithms encoded in the software in the microprocessor90. Electrodes 92 can be mounted on the surface skin of the user 70using transcutaneous electrical nerve stimulation equipment (TENS) orimplanted beneath the skin, using intramuscular implants or nerve cuffelectrodes. Selected muscles on which electrodes 92 are to be attachedfor neuromuscular stimulation to improve propulsion efficiency includehip flexor muscles, hip extensor muscles, trunk flexor muscles, trunkextensor muscles, abdominal muscles and combinations thereof.

The invention further encompasses a method of providing assistance touser 70 for manually propelling wheelchair 68. An example method isillustrated in FIGS. 8-14, and comprises:

-   -   detecting when user 70 has recovered from a previous push of the        wheels 72 of the wheelchair 68 (FIG. 8);    -   user 70 executing a next push of the wheels 72 (FIGS. 9-11);    -   applying neural stimulation to trunk and hip flexor muscles of        user 70 while the user executes the next push of the wheels;    -   detecting when the user has completed the next push of the        wheels (FIG. 11);    -   removing neural stimulation to the trunk and hip flexor muscles        of user 70 when the user has completed the next push of said        wheels (FIG. 11);    -   the user 70 recovering from the next push of said wheels (FIGS.        12-14);    -   applying neural stimulation to trunk and hip extensor muscles of        the user 70 while the user is recovering from the next push of        the wheels (FIGS. 12-14);    -   detecting when the user 70 has recovered from the next push of        the wheels (FIG. 8);    -   removing neural stimulation from the trunk and the hip extensor        muscles of the user 70 when the user has recovered from the next        push of the wheels (FIG. 8).

As illustrated in FIGS. 8-14, it is advantageous to apply neuromuscularstimulation to the trunk and hip flexor muscles while user 70 executes apush of wheels 72 because the pushing effort of the arms 80 is augmentedby the force and weight of the trunk 76 as it bends forward in flexion(FIGS. 9-11) in response to the stimulation. Similarly, it isadvantageous to remove the stimulation to the trunk and hip flexormuscles and apply stimulation to the trunk and hip extension muscles tocause extension of the trunk 76 (FIGS. 12-14) so that the user 70 mayrecover in preparation for the next push (FIG. 8). The timing of theapplication and removal of the neuromuscular stimulation depends upondetecting when user 70 has recovered and when the user has completed apush.

Detecting when user 70 has recovered from a push is effected bymeasuring a motion parameter of a part of the user while recovering.Practical motion parameters include a position of a part of the user, anacceleration of a part of the user, a rate of change of acceleration ofa part of the user and an electrical potential of a muscle of the user,as well as combinations of these motion parameters. The parts of theuser for which these motion parameters may be measured include the uppertrunk 76, the shoulder 78, the arm 80, the wrist 82, the head 84 andcombinations of these parts.

Detecting when user 70 has completed a push is effected by measuring amotion parameter of a part of the user while the user is pushing thewheels 72. Practical motion parameters include a position of a part ofthe user, an acceleration of a part of the user, a rate of change ofacceleration of a part of the user and an electrical potential of amuscle of the user, as well as combinations of these motion parameters.The parts of the user for which these motion parameters may be measuredinclude the upper trunk 76, the shoulder 78, the arm 80, the wrist 82,the head 84 and combinations of these parts.

Experimental evidence has shown that motion parameters of the wrist 82of user 70, specifically the anterior-posterior acceleration and rate ofchange of acceleration, in combination with medial-lateral accelerationand rate of change of acceleration of the wrist, are useful indetermining both the recovery from a push and the completion of a pushby the user. FIGS. 15 and 16 illustrate an example embodiment of analgorithm using these wrist motion parameters.

As shown in FIG. 15, detecting when user 70 has completed a push ofwheels 72 is effected by:

-   -   detecting an acceleration signal indicative of        anterior-posterior acceleration of a part of the user (wrist 82)        greater than a predetermined threshold value (94);    -   detecting an increasing rate of change of the acceleration        signal (96);    -   detecting a medial-lateral acceleration of the part of the user        (wrist 82) within a predetermined range of values (98).

As shown in FIG. 16, detecting when user 70 has recovered from a push iseffected by:

-   -   detecting an acceleration signal indicative of        anterior-posterior acceleration of a part of the user (wrist 82)        less than a predetermined threshold value (100);    -   detecting a decreasing rate of change of the acceleration signal        (102);    -   detecting a medial-lateral acceleration of the part of the user        (wrist 82) having an increasing rate of change (104).

Although it is expected that the motion parameters of other parts of theuser 70 may also be used to detect push completion and recovery, it hasbeen found effective to use the motion of the wrist 82 of the user 70 toexecute this algorithm.

It is expected that the systems and methods according to the inventionwill enhance a wheelchair user's experience, ability, efficiency andsafety.

What is claimed is:
 1. A wheelchair system providing neural stimulationto a user, said system comprising: a wheelchair; an inertial measurementunit positioned on said wheelchair for measuring a motion parameter ofsaid wheelchair and generating one or more signals indicative of saidmotion parameter; a plurality of neural stimulating electrodes, eachsaid electrode configured to be attached to a respective muscle of saiduser for activating said respective muscle; a controller incommunication with said inertial measurement unit and adapted to receivesaid signals, said controller also being in communication with saidplurality of electrodes configured for activating selected ones of saidrespective muscles in response to said signals; wherein said inertialmeasurement unit comprises at least one gyroscope and said motionparameter comprises an angular motion parameter.
 2. The wheelchairsystem according to claim 1, wherein said controller is mounted on oneof said wheelchair or said user.
 3. The wheelchair system according toclaim 1, wherein said inertial measurement unit comprises at least oneaccelerometer and said motion parameter comprises a linear motionparameter.
 4. The wheelchair system according to claim 3, wherein saidlinear motion parameter is oriented in a direction of motion of saidwheelchair, said linear motion parameter being selected from the groupconsisting of linear velocity, linear acceleration and combinationsthereof.
 5. The wheelchair system according to claim 4, wherein saidelectrodes are configured to be attached to said muscles selected fromthe group consisting of erector spinae, quadratus lumborum, gluteusmaximus, posterior adductor and combinations thereof.
 6. The wheelchairaccording to claim 5, wherein said electrodes are configured to beimplanted beneath skin of said user.
 7. The wheelchair according toclaim 5, wherein said electrodes are configured to be mounted on asurface of skin of said user.
 8. The wheelchair system according toclaim 1, wherein said angular motion parameter is oriented about aturning axis of said wheelchair, said angular motion parameter beingselected from the group consisting of angular acceleration, angularvelocity, and combinations thereof.
 9. The wheelchair system accordingto claim 8, wherein said electrodes are configured to be attached tosaid muscles selected from the group consisting of right erector spinae,right quadratus lumborum, right gluteus maximus, right posterioradductor, left erector spinae, left quadratus lumborum, left gluteusmaximus, left posterior adductor and combinations thereof.
 10. Thewheelchair system according to claim 9, wherein said electrodes areconfigured to be implanted beneath skin of said user.
 11. The wheelchairsystem according to claim 9, wherein said electrodes are configured tobe mounted on a surface of skin of said user.
 12. The wheelchair systemaccording to claim 1, wherein said inertial measurement unit comprises aradio frequency transmitter for wirelessly transmitting said signals tosaid controller.
 13. The wheelchair system according to claim 1, whereinsaid controller comprises a radio frequency receiver for receiving saidsignals and a microprocessor in communication with said receiver. 14.The wheelchair system according to claim 1, further comprising a seatbelt controlled by a motor mounted on said wheelchair, said controllercontrolling said motor for tightening said belt.
 15. The wheelchairsystem according to claim 1, further comprising a brake controlled by anactuator mounted on said wheelchair, said controller controlling saidactuator for applying said brake.
 16. The wheelchair system according toclaim 1, further comprising a distress indicator controlled by saidcontroller for broadcasting a distress call.
 17. A method of providingneural stimulation to at least one muscle of a user of a wheelchairbased upon motion of said wheelchair, said method comprising: measuringa motion parameter of said wheelchair using an inertial measurementunit; generating a signal indicative of said motion parameter;evaluating said signal; generating a stimulus configured to activatesaid at least one muscle of said user in response to said signal;wherein said inertial measurement unit comprises at least one gyroscopeand said motion parameter comprises an angular motion parameter.
 18. Themethod according to claim 17, wherein said measuring said motionparameter comprises measuring a linear velocity of said wheelchair. 19.The method according to claim 17, wherein said measuring said motionparameter comprises measuring a linear acceleration of said wheelchair.20. The method according to claim 17, wherein said measuring said motionparameter comprises measuring an angular acceleration of saidwheelchair.
 21. The method according to claim 17, wherein said measuringsaid motion parameter comprises measuring an angular velocity of saidwheelchair.
 22. The method according to claim 17, wherein saidgenerating a signal comprises generating a signal indicative of at leastone said motion parameter selected from the group consisting of a linearvelocity, a linear acceleration, an angular velocity, an angularacceleration, and combinations thereof.
 23. The method according toclaim 17, wherein said evaluating said signal comprises: converting saidsignal to a value indicative of a magnitude of said motion parameter;and comparing said magnitude to a threshold magnitude of said motionparameter.
 24. The method according to claim 17, wherein said evaluatingsaid signal comprises: converting said signal to a value indicative of adirection of said motion parameter; and comparing said direction to areference direction.
 25. The method according to claim 17, wherein saidgenerating said stimulus in response to said signal comprises: selectingsaid one or more muscles of said user; activating an electrodeconfigured to apply a neural stimulus configured to activate said one ormore muscles.
 26. The method according to claim 25, wherein saidselecting said one or more muscles of said user comprises selectingerector spinae, quadratus lumborum, gluteus maximus, and posterioradductor muscles when said motion parameter is a linear accelerationwhich exceeds a threshold value.
 27. The method according to claim 25,wherein said selecting said one or more muscles of said user comprisesselecting right erector spinae, right quadratus lumborum, right gluteusmaximus, and right posterior adductor muscles when said motion parameteris an angular acceleration or an angular velocity in a counterclockwisedirection about a turning axis.
 28. The method according to claim 25,wherein said selecting said one or more muscles of said user comprisesselecting left erector spinae, left quadratus lumborum, left gluteusmaximus, and left posterior adductor muscles when said motion parameteris an angular acceleration or an angular velocity in a clockwisedirection about a turning axis.